As of now I have always been working with Java (when it comes to the JVM) and haven’t had the reason to use Kotlin.
But I have thought about using it in multiple scenarios, both at work and personally.

When it comes to our company’s ecosystem it is a bit more complicated. Most of our developers can work with one of the “main” languages in our company; Java, PHP, NodeJS, “Angular”, C, Python and Bash. With that it makes it hard to work with for example: Kotlin, as it is listed in our skillset at job openings.
Having said that, even though it is rather hard to switch to a new language, it has happened. Sadly enough not a lot, and most of the time with projects outside of our regular paycheck. For example: internal Android applications and or programs that are only for internal usage with the only criteria being: “it has to be understandable and a supported language that atleast 1 person in the company knows or has been doing research about (and can show that).”

So to the conclusion: its a bit double weither or not to work with Kotlin (or any other language outside of our skillset) as it does happen but depends on personal interest and personal investment. It doesn’t happen inside of the box. I have thought about it, but havent been able to think of a project that I wan’t to adapt internally.

Understood. Thanks for comprehensive answer! If you'll ever work on your own open-source project, I would highly recommend to try Kotlin. You'll see the benefits and its cool features (taken form Node, Python, Ruby, Shell etc.) in a very short time, I can guarantee you that ;)